Oil-Based Ink Composition for Ink Jet Recording and Method for Inspecting It

ABSTRACT

The invention provides an oil-based ink composition for ink jet recording, which is best suited for printing onto polyvinyl chloride substrates, and improved in terms of both the stabilities of ink on storage and jetting, and a method for inspecting the same. The oil-based ink composition for ink jet recording comprises as a main solvent at least a specific polyalkylene glycol dialkyl ether and containing at least a specific quinacridone pigment component. That composition should be such that when a measuring sample comprising it is analyzed by means of high speed liquid chromatography under specific measuring conditions, the concentration of a component having a peak at the holding time of 10.3 minutes is 0.4 ppm or less.

ART FIELD

The present invention relates to an oil-based ink composition for inkjet recording and a method for inspecting it.

BACKGROUND ART

Among various ink jet recording modes known so far in the art, there area mode of jetting ink using electrostatic induction force (electricfield control mode), a mode of jetting ink using the driving pressure ofa piezoelectric device (drop-on-demand mode or pressure pulse mode), anda mode of generating and growing bubbles by high heat thereby jettingink through the resulting pressure (bubble or thermal jet mode), bywhich images of very high precision can be obtained.

Inks used with such ink jet recording modes generally include awater-based ink using water as a main solvent, and an oil-based inkusing an organic solvent as a main solvent. Printed images obtainedusing the water-based ink are generally poor in water resistance, andthat water-based ink renders it difficult to print images on a recordingmedium having a water-resistant surface. On the other hand, theoil-based ink has the merits of being capable of providing printedimages excelling in water resistance, and making it easy to print imageson a recording medium or wood free paper having a water-resistancesurface. An oil-based ink using a pigment as a coloring material is alsoexcellent in light fastness. Conventional oil-based inks make use ofaromatic hydrocarbons such as toluene or xylene, aliphatic hydrocarbonssuch as hexane or kerosene, ketones such as methyl ethyl ketone, esterssuch as ethyl acetate, or solvents such as propylene glycol monomethylether acetate. Problems with such inks are, however, that their fastdrying due to low boiling points or flash points are likely to clog upnozzles, and they render printer specifications costly for the reasonsof their solubility and swell capability in plastics (for instance,polystyrene resin or ABS resin) used for ink storage containers, andprinters or like apparatus or parts thereof. When images are printed ona polyvinyl chloride substrate, there is another problem arising aboutimage quality and printed image dry capability.

The inventors have already come up with an oil-based ink composition forink jet recording, which comprises polyalkylene glycol dialkyl eithersolvent as a main solvent and further contains a carbon black pigment, abinder resin and a dispersant so that it is fit for printing onto apolyvinyl chloride substrate. However, it has now been found that whenthat oil-based ink composition contains a quinacridone pigment, thestability of ink on storage become worse due to crystallization and theoccurrence of deposits such as coarse particles, and there is a problemarising about the stability of ink on ink jetting.

For a conventional water-based ink composition containing a quinacridonepigment and a water-based organic solvent such as alcohols or carbitols,it has been proposed to selectively use a water-based organic solventwhose solubility in the quinacridone pigment itself is less dependent ontemperature, thereby eliminating or reducing the crystallization of thepigment or the amount of deposits such as coarse particles (see PatentPublication 1). When it comes to an ink composition containing apolyalkylene glycol dialkyl ether solvent as a main solvent, however,the solubility of that solvent in the quinacridone pigment does notlargely change unlike the water-mixed solvent in Patent Publication 1,although depending on the type of the solvent. In other words, it hasbeen found that a similar inspection method as described in PatentPublication 1 cannot be used as an index to a reduction in deposits thataffect the stabilities of the oil-based ink on storage and ink jetting.

Patent Publication 1

JP(A)2003-268265

SUMMARY OF THE INVENTION

The primary object of the invention is to provide an oil-based inkcomposition for ink jet recording, which comprises a polyalkylene glycoldialkyl ether solvent as a main solvent and further contains aquinacridone pigment, and which is improved in terms of the stabilitiesof ink on storage and ink jetting as well as an inspection method for anoil-based ink composition for ink jet recording, which is capable ofpre-assessing how much risk there is of recrystallization and depositssuch coarse particles occurring.

According to the invention, that object is achievable by the provisionof an oil-based ink composition for ink jet recording, comprising as amain solvent at least a polyalkylene glycol dialkyl ether represented bythe following general formula (1) and containing at least a pigmentcomponent represented by the following general formula (2),characterized in that when a measuring sample prepared by adding 2 ml ofN-methyl-2-pyrrolidone and 8 ml of acetonitrile to 100 mg of saidoil-based ink composition is analyzed by means of high speed liquidchromatography under the following measuring conditions, theconcentration of a component having a peak at a holding time of 10.3minutes is 0.4 ppm or less:

R¹¹—(OR¹³)_(n)—OR¹  General Formula (1)

where R¹¹ and R¹² that may be identical with or different from oneanother, are each an alkyl group having 1 to 3 carbon atoms, R¹³ is anethylene or propylene group, and n is an integer of 2 to 4;

where R stands for a hydrogen atom, a methyl group or a chlorine atom;and

Measuring Conditions for High Speed Liquid Chromatography

an ODS column of 4.6 mm in inner diameter and 25 cm in length is used;water (liquid A)/acetonitrile (liquid B) is used as an eluting solutionat a flow rate of 1.0 ml/min. and at such a mixing ratio that there islinear gradient elution occurring, wherein the eluting solution flows ata constant 50% by volume/50% by volume (A/B) from the start of elution(0 minute) to the elapse of 1 minute, and at a rate varying from 50% byVolume/50% by volume (A/B) to 0% by volume to 100% by volume (A/B) fromthe elapse of 1 minute after the start of elution to the elapse of 25minutes; the column temperature is at 40° C.; and the detectionwavelength is at 254 nm±4 nm.

The aforesaid oil-based ink composition for ink jet recording is alsocharacterized by further containing a lactone solvent, a binder resinand a dispersant.

The present invention also provides an inspection method for anoil-based ink composition for ink jet recording, which comprises as amain solvent at least a polyalkylene glycol dialkyl ether represented bythe aforesaid general formula (1) and as a composition component atleast a pigment component represented by the aforesaid general formula(2), characterized in that said oil-based ink composition is assessed asapplicable to ink jet recording when, in analyzing a measuring sampleprepared by adding 2 ml of N-methyl-2-pyrrolidone and 8 ml ofacetonitrile to 100 mg of said oil-based ink composition by means ofhigh speed liquid chromatography under the aforesaid measuringconditions, the concentration of a component having a peak at a holdingtime of 10.3 minutes is 0.4 ppm or less.

BRIEF DESCRIPTION OF THE DRAWING

The purposes and advantages of the invention will be apparent from thefollowing detailed description in conjunction with the appended singledrawing.

FIG. 1 is indicative of chromatograms for the oil-based ink compositionsfor ink jet recording as obtained in Examples 1 and 4 as well asComparative Example 3.

BEST MODE OF CARRYING OUT THE INVENTION

The composition of the oil-based ink composition for ink jet recordingaccording to the invention is now explained.

The solvent in the oil-based ink composition comprises as its mainsolvent the polyalkylene glycol dialkyl ether having the aforesaidgeneral formula (1). The polyalkylene glycol dialkyl ether having theaforesaid general formula (1) has a boiling point of 150° C. or higher,and preferably 180° C. or higher under atmospheric pressure. Althoughthere is no upper limit provided to the boiling point, yet it ispreferable that the ether has a prime facie upper limit boiling point ofabout 240° C. in view of the ink jetting recording function or the etherhas to have a high boiling point and a low vapor pressure and beimproved in terms of work-site safety as well. The ether according tothe invention has also a density of 0.9 g/cm³ to 1.0 g/cm³ at 20° C.

The polyalkylene glycol dialkyl ether here, for instance, includesdiethylene glycol dimethyl ether, triethylene glycol dimethyl ether,tetraethylene glycol dimethyl ether, diethylene glycol diethyl ethertriethylene glycol diethyl ether, tetraethylene glycol diethyl ether,diethylene glycol ethyl methyl ether, triethylene glycol ethyl methylether, tetraethylene glycol methyl methyl ether, diethyleneglycol-di-n-propyl ether and diethylene glycol-di-iso-propyl ether,among which preference is given to diethylene glycol diethyl ether,triethylene glycol dimethyl ether and diethylene glycol ethyl methylether.

For the solvent component it is preferable to use a lactone solvent incombination with the main solvent. The lactone solvent is a compoundhaving a ring structure by way of an ester bond, including, forinstance, γ-lactone having a five-membered ring structure, δ-lactonhaving a six-membered ring structure, and ε-lactone having aseven-membered ring structure. More specifically, there is the mentionof γ-butyrolactone, γ-valerolactone, γ-hexylactone, γ-heptalactone,γ-octalacctone, γ-nonalactone, γ-decalactone, γ-undecalactone,δ-valerolactone, δ-hexylactone, δ-heptalactone, δ-octalacctone,δ-nonalactone, δ-decalactone, δ-undecalactone, and ε-caprolactam.

In a preferable embodiment of the invention, the lactone solvent isγ-lactone having a five-membered ring structure, and in a morepreferable embodiment, the lactone solvent is γ-butyrolactone, andγ-valerolactone.

Referring here to the proportion of the ether and lactone solvents, itis preferable that the lactone solvent is used in an amount of 0.02 to 4parts by mass, especially 0.05 to 2 parts by mass per 1 part by mass ofthe polyoxyethylene glycol dialkyl ether having the general formula (1).The ether and lactone solvents are preferably contained in the oil-basedink composition in an amount of at least 50% by mass, and preferably atleast 70% by mass. This ensures the improved ability of the ink topenetrate through a polyvinyl chloride substrate, the improved levelingcapability, and the improved image drying capability.

Reference is then made to the component that is to be dispersed ordissolved in the aforesaid ether and lactone solvents in the oil-basedink composition for ink jet recording.

The coloring material here is a quinacridone pigment having theaforesaid general formula (2). The primary particles of the pigment havea volume-average particle diameter of 50 to 500 nm, and preferably 50 to200 nm. The content of the pigment is 0.5 to 25% by mass, preferably 0.5to 15% by mass, and more preferably 1 to 10% by mass in the oil-basedink composition.

A variety of quinacridone pigments are now on the market. However, ithas now been found that although depending on the makers and productionlots of such quinacuridone pigments, there are deposits whose solubilityin the solvents of the invention depends on temperature, and acoarsening of such deposits has adverse influences on the stabilities ofink on storage and ink jetting. In consideration of the fact that thedeposits differ depending on the makers and production lots ofquinacridone pigments, the quinacridone pigment used is going to containa component of raw materials or the like in the production process. Thiscomponent whose solubility depends on temperature could possibly causedeposits to occur due to recrystallization and coarsening.

Details of the deposits have yet to be clarified. From the results ofhigh speed liquid chromatography (HPLC) of collected deposits, however,the inventors have now found that there is a chromatogram obtainedhaving a peak at the holding time of around 10.3 minutes alone, and thatthe component having a peak at the holding time of 10.3 minutes matcheswith those deposits. FIG. 1 is indicative of chromatograms for theoil-based ink compositions for ink jet recording obtained in Examples 1and 4 as well as Comparative Example 3. In Examples 1 and 4 andComparative Example 3, the concentration of the component having a peakat the holding time of 10.3 minutes is found to be 0.08 ppm, 0.36 ppm,and 1.40 ppm, respectively. It is noted that FIG. 1 has peak strength(AU) as ordinate. If deposits are collected to prepare compositions ofvarying concentrations and they are likewise analyzed by means of HPCLto make analytical curves, it is then possible to calculate strength asconcentration using those analytical curves. Although where peaks atholding times except 10.3 minutes in FIG. 1 assign to still remainunclear, there could be no correlation to the deposits in view of thechromatogram of the deposits alone.

The consideration of the examples given later teaches that an oil-basedink composition wherein the concentration of the component having a peakat the holding time of 10.3 minutes is 0.4 ppm or less can provide anoil-based ink composition for ink jet recording that can be much moreimproved in terms of stability on storage and ink jetting, because ofbeing free of any coarse particles. The present invention also providesa method for the inspection of an oil-based ink composition for ink jetrecording that can pre-assess it about how much risk there is ofrecrystallization and a coarsening of particles. It is here noted thatthe detectable lowest concentration (detection sensitivity) of thecomponent having a peak at the holding time of 10.3 minutes is 0.05 ppm.

Besides the quinacridone pigment, the oil-based ink composition for inkjet printing according to the invention further contains a binder resinand a dispersant optionally in a dispersed or dissolved state.

The binder resin here is soluble in the organic solvent such as thepolyalkylene glycol dialkyl ether, and added to the oil-based inkcomposition for the purpose of controlling its viscosity and the abilityof ink to be fixed to a polyvinyl chloride substrate. The binder resin,for instance, includes acrylic resin, styrene-acrylic resin,rosin-modified resin, phenolic resin, terpene resin, polyester resin,polyamide resin, epoxy resin, vinyl chloride-vinyl acetate copolymerresin, cellulosic resin such as cellulose acetate butyrate, andvinyltoluene-a-methylstyrene copolymer, which may be used alone or inadmixture.

The content of the binder resin is 0.5 to 10 times, and preferably 0.75to 7 times as much as the content of the quinacridone pigment (on weightbasis).

For the dispersant, use may be made of any desired dispersant employedwith ordinary oil-based ink compositions, especially with oil-based inkcompositions for ink jet recording. Preference is given to a polymerdispersant comprises as a main chain a polyester chain, a polyacrylicchain, a polyurethane chain or a polyamine chain and as a side chain apolar group such as an amino group, a carboxyl group, sulfone group orhydroxyl group, and a polyester-based polymer dispersant is particularlypreferred. For the dispersant, it is preferable to use a dispersant thattakes effect when the solubility parameter of the organic solvent is inthe range of 8 to 11.

For such dispersants, commercially available ones may be used. Specificexamples are polyester-based polymer compounds such as Hinoact SeriesKF1-M, T-6000, T-7000, T-8000, T-8350P, and T8000EL (made by Takefu FineChemical Co., Ltd.); Solsperse Series 20000, 24000, 32000, 32500, 33500,34000, and 35200 (Lubrizol Corporation.); Disperbyk Series 161, 162,163, 164, 166, 180, 190, 191 and 192 (made by BYK Chemie Co., Ltd.);Flowlen DOPA Series 17, 22, 33, and G-700 (Kyoei Chemical Co., Ltd.);Ajispar Series PB821, and PB711 (made by Ajinomoto Fine Techno Co.,Ltd.); and LP Series 4010, LP4050, LP4055, POLYMER Series 400, 401, 402,403, 450, 451, and 453 (Efka Chemicals Co., Ltd.), which may be usedalone or in admixture.

The content of the dispersant(s) in the oil-based ink composition of theinvention is 5 to 200% by mass, and preferably 30 to 120% by massrelative to the content of the quinacridone pigment.

The oil-based ink composition of the invention may additionally containantioxidants, ultraviolet absorbers, and surfactants. A typicalantioxidant is BHA (2,3-butyl-4-hydroxyanisole), and BHT(2,6-di-t-butyl-p-cresol), and added to the oil-based ink composition inan amount of 0.01 to 3.0% by mass. A typical ultraviolet absorber is abenzophenone or benzotriazole compound, and added to the oil-based inkcomposition in an amount of 0.01 to 0.5% by mass. The surfactant usedmay be any of anionic, cationic, amphoteric or nonionic ones, and isadded to the oil-based ink composition in an amount of 0.5 to 4.0% bymass.

If required or optionally, additives such as plasticizers, anti-staticagents, viscosity modifiers and defoaming agents may be added to theoil-based ink composition for ink jet recording according to theinvention.

The oil-based ink composition for ink jet recording according to theinvention may be prepared or otherwise formulated by adding thequinacridone pigment and dispersant to a part of the organic solventsuch as the polyalkylene glycol dialkyl ether, and then mixing anddispersing them by means of ball mills, bead mills, ultrasonic waves,jet mills or the like to prepare a pigment dispersion. Then, the rest ofthe aforesaid solvent, the binder resin and other additives are addedunder agitation to the obtained pigment dispersion.

The thus obtained oil-based ink composition for ink jet recording isadjusted in such a way as to have a viscosity of 2 to 10 mPa·s, andpreferably 3 to 5 mPa·s, as measured at 20° C.

The oil-based ink composition of the invention has preferably a surfacetension of 20 to 50 mN/m. As the surface tension falls short of 20 mN/m,it will often cause the ink composition to spread over the surface ofthe head of a printer for ink jet recording, or ooze out, rendering thejetting of ink droplets difficult. As the surface tension exceeds 50mN/m, it will often result in the inability of the ink composition tospread over the surface of a recording medium, rendering satisfactoryprinting impossible.

For instance, the oil-based ink composition of the invention, because ofhaving the merit of being inert to the surface of an ink-repellent jetnozzle, is favorably used with an ink jet recording process wherein inkis jetted from a printer head for ink jet recording that has anink-repellent jet nozzle surface.

The oil-based ink composition for ink jet recording according to theinvention is preferably applicable to a recording medium comprising aplastic substrate, especially a hard or soft polyvinyl chloridesubstrate exemplified by a polyvinyl chloride film or sheet. With theoil-based ink composition for ink jet printing, it is possible to applyprinting to an unprocessed surface of the polyvinyl chloride substrateand, hence, dispense with any costly recording medium like aconventional recording medium having an ink receiving layer, although itmay be applied to an application surface treated by an ink receivingresin.

Example

By way of example but not by way of limitation, the present invention isnow explained with reference to specific examples.

It is noted that viscosity was measured with a viscometer “AMVn” made byAnton Paar Co., Ltd, and the particle diameter of pigment particles wasmeasured with “MicroTrack UPA150” made by Nikkiso Co., Ltd.

Inventive and Comparative Examples

Seven commercial quinacridone pigments (C.I. Pigment Red 122) whereinthe R in the general formula (2) was a methyl group, varying in makersand production lots, were readied up for experimentation.

To a part of the solvent composed of

Diethylene glycol diethyl ether 72.5 parts by mass γ-butyrolactone 20parts by mass3 parts by mass of one of the aforesaid pigments (C.I. Pigment Red 122)and 1.5 parts by mass of a dispersant (“Solsperse 32000” made byLubrizol Corporation) were added for one hour stirring at 3,000 rpm in adissolver, followed by pre-dispersion in a bead mill charged withzirconia beads (2 mm). The obtained pigment particles had an averageparticle diameter of 5 μm or less. Further, dispersion was carried outwith a nano-mill charged with zirconia beads (0.3 mm) to obtain apigment dispersion found to have an average pigment particle diameter of150 nm.

Under stirring at 4,000 rpm, 3 parts by weight of a binder resin(“Paraloid B60” made by Rohm and Haas Co., Ltd.) and the rest of theaforesaid solvent were added to the obtained pigment dispersion toprepare an oil-based ink composition for ink jet recording. Theviscosity of the composition is set out in Tables 1 and 2.

The remaining six of the aforesaid C.I. Pigment Red 122 were similarlyformulated into oil-based ink compositions for ink jet recording. Theviscosities of the respective compositions are again set out in Tables 1and 2.

HPLC (Preparation of the Measuring Sample)

One hundred (100) mg of each oil-based ink composition are placed in a30 ml vial bottle, and 2 ml of N-methyl-2-pyrrolidone are added to andmixed with the composition, to which 8 ml of acetonitrile are furtheradded. The obtained solution is filtered through a 45-μm hydrophilicPTFE membrane filter Milleex-LH (Nippon Millipore Co. Ltd.). Five (5) μlof the filtrate were collected to obtain a measuring sample.

(Measuring Conditions)

An HPLC analyzer (2695/2996 made by Nippon Waters Co., Ltd.) and an ODScolumn for HPLC (Supelco sil LC-18 DB Column of 4.6 mm in inner diameterand 25 cm in length made by Supelco Co., Ltd.) were used with an elutingsolution of water (liquid A)/acetonitrile (liquid B) at a flow rate of1.0 ml/min. Linear gradient elution was carried out such that the mixingratio of the eluting solution was kept at a constant 50% by volume/50%by volume (A/B) from the start of elution (0 minute) to the elapse ofone minute, and varied from 50% by volume/50% by volume (A/B) to 0% byvolume to 100% by volume (A/B) from the elapse of one minute after thestart of elution to the elapse of 25 minutes. Measurement was done at acolumn temperature of 40° C. and a detection wavelength of 254 nm±4 nm.

As the ODS column here, Supelco sil LC-18 DB column (made by Spelco Co.,Ltd.) was used; in the invention, however, any of commercial ODScolumns, for instance, Develo sil ODS-HG (made by Nomura Chemical Co.,Ltd.), may preferably be used.

FIG. 1 is indicative of the chromatograms for the oil-based inkcompositions obtained in Examples 1 and 4 as well as Comparative Example3.

Using the chromatogram obtained using each oil-based ink composition andseparately created analytical curves (not shown), the concentration ofthe component having a peak at the holding time of 10.3 minutes wasfound. The results are set out in the form of detected concentrations(ppm) in Tables 1 and 2.

(Stability on Storage (1μ Foreign Matters))

Each oil-based ink composition was placed in a polypropylene samplevessel that was then tightly lidded up. In this state, the compositionwas let stand alone in a room temperature environment for one week,after which it was filtered through a 1μ glass filter to observe 1μforeign matters. The results are set out in the “stability on storage(1μ foreign matters)” in Tables 1 and 2.

(Stability on Storage (Coarse Particles))

After heated to 90° C. or higher, each oil-based ink composition was letstand alone and cooled off in a room temperature environment. By givingsuch hysteresis to the oil-based ink composition, a lot more dissolublecomponent was dissolved to accelerate recrystallization. This is toassess the risk of deposition more rapidly than at room temperature.After let stand alone, the oil-based ink composition was filteredthrough a 1μ glass filter to observe coarse foreign matters of 5μ orgreater. The results are set out in the “stability on storage (coarseparticles)” in Tables 1 and 2.

(Stability on Jetting)

Each oil-based ink composition was loaded in an ink jet printer(MJ-8000C made by Seiko Epson Corporation) to apply continued printingto a polyvinyl chloride film (Viewcal made by Lintec Co., Ltd.) for thepurpose of observing the occurrence of foreign matters in the printer.The results are set out in the “stability on jetting” in Tables 1 and 2.

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Viscosity of the composition 4.1 4.0 4.24.0 (mPa · s (20° C.)) Detected concentration (ppm) 0.08 0.12 0.25 0.36Stability on storage none none none none 1μ foreign matters Coarseparticles none none none none Stability on jetting none none none noneForeign matters in the Printer

TABLE 2 Comparative Example 1 2 3 Viscosity of the composition 4.2 4.13.9 (mPa · s (20° C.)) Detected concentration (ppm) 0.50 0.88 1.40Stability on storage found found found 1μ foreign matters Coarseparticles found found found Stability on jetting found found foundForeign matters in the Printer

From Tables 1 and 2, it is appreciated that as long as the detectedconcentration remains 0.4 ppm or less, both the stability on storage andthe stability on jetting are improved. It is also found that wheneverthere is an oil-based ink composition having a detected concentrationexceeding 0.4 ppm can be assessed as being not applied to ink jetrecording, and the invention provides a favorable method for theinspection of oil-based ink compositions for ink jet recording.

The oil-based ink composition for ink jet recording according to theinvention is best suited for printing onto polyvinyl chloridesubstrates, and is more improved than ever in terms of stability of inkon storage and jetting.

1. A process of producing an oil-based ink composition for ink jetrecording, in which at least a pigment component represented by thefollowing general formula (2) is dispersed in a mixed solvent comprisinga polyalkylene glycol dialkyl ether represented by the following generalformula (1) and a lactone solvent in an amount of 0.02 to 4 parts bymass per 1 part by mass of said ether into an oil-based ink composition,characterized in that when a measuring sample prepared by adding 2 ml ofN-methyl-2-pyrrolidone and 8 ml of acetonitrile to 100 mg of saidd-based ink composition is analyzed by means of high speed liquidchromatography under the following measuring conditions, theconcentration of a component having a peak at a holding time of 10.3minutes is set at 0.4 ppm or less:R¹¹—(OR¹³)_(n)—OR¹  General Formula (1) where R¹¹ and R¹² that may beidentical with or different from one another, are each an alkyl grouphaving 1 to 3 carbon atoms, R¹³ is an ethylene or propylene group, and nis an integer of 2 to 4;

where R stands for a hydrogen atom, a methyl group or a chlorine atom;and Measuring Conditions for High Speed Liquid Chromatography an ODScolumn of 4.6 mm in inner diameter and 25 cm in length is used; water(liquid A)/acetonitrile {liquid B) is used as an eluting solution at aflow rate of 1.0 ml/min and at such a mixing ratio that there is lineargradient elution occurring, wherein the eluting solution flows at aconstant 50% by volume/50% by volume (A/B) from the start of elution (0minute) to the elapse of 1 minute, and at a rate varying from 50% byvolume/50% by volume (A/B) to 0% by volume to 100% by volume (A/B) fromthe elapse of 1 minute after the start of elution to the elapse of 25minutes; the column temperature is at 40° C.; and the detectionwavelength is at 254 nm±4 nm.
 2. The process for producing an oil-basedink composition for ink jet recording according to claim 1,characterized by further containing a binder resin, and a dispersant. 3.(canceled)